This invention relates to an enclosed type compressor to be used for a refrigerating system, for example, and a method for assembling the same.
An enclosed type compressor constructed such that an electric motor and a compressor pump assembly driven by the electric motor are enclosed in a sealed casing has been widely known. In such a compressor, the electric motor and the compressor pump assembly are ordinarily produced separately and then assembled together within the casing. In this case, the rotor of the electric motor is firstly connected with the driving shaft of the compressor pump assembly and then is inserted into the stator of the electric motor secured to the internal surface of the casing with a narrow air gap maintained between the outer surface of the rotor and the inner surface of the stator.
When the air gap is uneven, the rotor of the electric motor is urged toward a side having a narrower air gap, thus increasing the starting torque of the electric motor. Increased starting torque requires a starting apparatus of a large capacity, and in the worst case a larger size electric motor having an increased air gap, thus reducing the efficiency and power factor of the electric motor.
U.S. Pat. Nos. 3,850,551 and 3,872,562 disclose enclosed type compressors and methods for assembling the compressors wherein the stator of the electric motor is secured directly to the internal surface of a casing, while the compressor pump assembly is secured to a plate disposed perpendicular to the internal surface of the casing. During the assembling, the center-adjusting operation of the electric motor is carried out by use of a gap gauge, mandrel and the like. In this manner, although a plate is disposed perpendicular to the internal surface of the casing, the plate is not always perpendicular to the internal surface of the stator, and hence the central axis of the rotor tends to be inclined against the internal surface of the stator.
Although the internal surface of the casing is ordinarily machined cylindrically, the surface thereof tends to be deformed from a true cylindrical configuration because of irregularities in the material (particularly in the elongation property thereof) and as a result of welding or fitting of gas discharging and returning pipes, legs of a terminal block and the like to the casing, thus rendering the measurements of the internal surface of the casing to be inaccurate. Furthermore, the internal surface of the stator tends to be eccentric relative to the outer surface thereof due to the laminated construction of the stator, and for this and the above described reasons, the central axis of the internal surface of the stator tends to be misaligned with that of the casing. When the electric motor and the compressor pump assembly are assembled together with reference to the internal surface of the casing, the above described misalignment causes an air gap between the stator and the rotor to be uneven. Furthermore, the center adjusting operation utilizing the gap gauge or mandrel is difficult to be carried out automatically, thus requiring a long time and entailing drawbacks of accompanying large center adjusting errors. Since the above described center adjusting operation is advantageously carried out through an opening provided at an end of the casing remote from the compressor pump assembly, two openings are required to be provided through the casing at upper and lower ends thereof. The provision of two openings, however, requires further welding of cover plate to close the opening, and in consideration of the thermal effects, the spacing between the cover and various parts within the casing must be increased, thus increasing the size of the enclosed type compressor.